The invention relates to a master cylinder for a hydraulic vehicle braking system with a housing and a bore formed therein, in which bore a first piston and a second piston, which is arranged at an axial distance from the first piston, are carried in a sealing and displaceable manner, and with a restraining device, which is arranged between the first piston and the second piston, for a return spring of the first piston, which device prevents the return spring from being compressed and expanded beyond a certain extent. Master cylinders of this kind, which are also called transmitter cylinders, are used in a vast number of cases and are known, for example, from DE 195 20 670 A1.
The restraining device for the return spring of the first piston ensures on the one hand that a defined distance between the two pistons is re-established when the master cylinder is relieved of pressure, so that the two pistons are accurately positioned relative to one another in their rest position, and on the other that, should a pressure loss occur in the primary pressure chamber, on which the first piston acts, of the master cylinder due, for example, to a leak, a brake pressure is built up as quickly as possible in the secondary pressure chamber, which may still be operative and on which the second piston acts, by the restraining device producing a rigid through-drive between the first piston and the second piston (fail safe function) after the return spring of the first piston has been compressed beyond a predetermined value.
Known restraining devices of the described type are of a relatively complicated structure and take a long time to assemble. For example, the restraining device known from DE 195 20 670 A1 consists of two sheet-metal sleeves which are of a U-shaped cross section and are connected together by a spacer pin. At one end this spacer pin has a widened head, which positively interacts with one sheet-metal sleeve. The spacer pin is connected to the other sheet-metal sleeve by placing an annular fixing element on the corresponding end of the spacer pin and then riveting the fixing element to the spacer pin by deforming the part of the latter which still protrudes. This can only take place after the restraining device has been assembled, and the restrained return spring must also be significantly compressed by a separate appliance, as the end of the spacer pin must project out of the sheet-metal sleeve in order to carry out the riveting process. Moreover, this kind of fixing process results in considerable tolerances on the length of the restraining devices.
The object of the invention is to provide a master cylinder whose restraining device is simple to produce and easy to assemble and which also has improved accuracy of length.
This object is achieved according to the invention by a master cylinder whose restraining device has the features presented in claim 1. In contrast to the prior art, the restraining device of the master cylinder according to the invention only consists of two components, a first, substantially sleeve-shaped component and a second, substantially pin-shaped component. These two components can be coupled together by a simple joining action though the flange on the pin-like component and the first receiving flange, which interacts with the latter flange, on the sleeve-shaped component as well as the lateral introduction opening in the sleeve-shaped component, which communicates with the open region of the first receiving flange.
The introduction opening in the circumferential surface area of the sleeve-shaped component, which must be of a size at least at one point such that the flange provided on the pin-shaped component fits through it, may be arranged either near or even adjacent to the open region of the receiving flange or else remote therefrom. If the introduction opening is axially remote from the receiving flange, the opening cross section of the cut-out, which connects the introduction opening to the receiving flange, in the circumferential surface area of the sleeve-shaped component may be designed smaller than the opening cross section of the introduction opening, thus providing lateral guidance for the flange of the pin-shaped component which is inserted in the sleeve-shaped component, this guidance preventing the flange from being pushed out of the sleeve-shaped component.
According to a preferred development of the master cylinder according to the invention, the end of the sleeve-shaped component which is remote from the pin-shaped component comprises a second, U-shaped receiving flange which projects radially inwards and which positively interacts with a flange on the second piston which projects radially outwards. In order that the flange provided on the second piston may be joined to the sleeve-shaped component, the latter comprises in its circumferential surface area an introduction opening which communicates with the open region of the second receiving flange and which enables the flange to be laterally introduced into the sleeve-shaped component. If the introduction opening described above, which is axially remote from the first receiving flange, is arranged adjacent to the second receiving flange, then this introduction opening may serve to introduce both the flange provided on the pin-shaped component and the flange provided on the second piston into the sleeve-shaped component (in this order).
It is, however, also possible to provide two introduction openings in the sleeve-shaped component, one of which communicates with the open region of the:first receiving flange and the second of which communicates with the open region of the receiving flange. These two introduction openings may be arranged on the same side or on opposite sides of the sleeve-shaped component.
The two U-shaped receiving flanges may similarly open towards the same side or towards opposite sides of the sleeve-shaped component. If both receiving flanges open towards the same side of the sleeve-shaped component, thenxe2x80x94according to one embodiment of the restraining device of the master cylinder according to the inventionxe2x80x94a single introduction opening extends in the circumferential surface area of the sleeve-shaped component from the open region of the first receiving flange to the open region of the second receiving flange. In another embodiment, in which the two receiving flanges likewise open towards the same side of the sleeve-shaped component, there are two introduction openings which are separated from one another by a portion of the circumferential surface of the sleeve-shaped component. This circumferential surface portion improves the stability of the sleeve-shaped component and at the same time represents a lateral guide for the flange provided on the pin-shaped component when it is introduced into the sleeve-shaped component and the return spring is compressed.
In all embodiments of the master cylinder according to the invention the first U-shaped receiving flange or the second U-shaped receiving flange or even both receiving flanges of the sleeve-shaped component may each comprise one or more latching projections which, after the pin-shaped component has been joined to the first receiving flange or the flange provided on the second piston has been joined to the second receiving flange, prevent(s) or at least oppose(s) an automatic disengagement of the established connection in the lateral direction.
The circumferential surface of the sleeve-shaped component may also comprise one or more apertures in all embodiments of the master cylinder according to the invention in order to improve the flow of hydraulic fluid through the restraining device. This kind of formation makes it easier to fill the above-mentioned primary pressure chamber of the master cylinder, in which the restraining device is located, with hydraulic fluid. In the extreme case the sleeve-shaped component may be reduced to its two receiving flanges and a plurality (at least two) of axial web-shaped connections between these two receiving flanges. The web-shaped connections between the two receiving flanges are then arranged so as to ensure that the sleeve-shaped component is sufficiently stable.
According to one development, in all embodiments the pin-shaped component may comprise, at its end which is remote from the sleeve-shaped component, a bore which is entered by a stud, bonded or welded to this bore, of a spring holding head. This kind of formation of the pin-shaped component enables the maximum length of the restraining device to be adjusted with utmost accuracy and then fixed when assembling the restraining device.